The United Kingdom raised its terrorism threat level to critical, the highest level possible, Saturday after a vehicle plowed into the terminal building at Scotland’s busiest airport and burst into flames.

Police at the highest levels are assuming the fiery incident in Glasgow was a terrorist attack, CNN has learned.

Authorities assume the incident is linked to the discovery Friday in London of two explosives-filled cars. They could not yet say whether the same people were involved or whether the Glasgow incident was the work of copycats.

Police and witnesses in Glasgow described an SUV-style vehicle in flames being driven at full speed toward the building.

Two people were arrested at the scene, police said.

It was not immediately clear whether there were any injuries, although unconfirmed witness reports described a man on fire at the scene.

Glasgow Airport has been closed and all flights have been suspended. All roads around the airport have been closed.
Operators BAA Scotland warned people not to travel to the airport “until further notice”.
Edinburgh Airport was also closed to vehicles, though flights are operating as normal. Security has been stepped up at Glasgow Central railway station.

BAA Scotland spokesman Donald Morrison said that 35,000 passengers had been expected through Glasgow Airport during the course of Saturday, the first full day of the school summer holidays.

Travellers evacuated from the airport were being looked after at nearby hotels as uncertainty over their flight plans remained.

A number of people are believed to be stuck on airplanes and on the airport strip while others have been told they might not be able to leave the airport complex until at least 2100 BST.

Prestwick Airport was operating as normal. Flights bound for Glasgow Airport had been diverted to Prestwick.